Recently, particles have been applied to various industrial fields. The applications have increased year by year, for example, catalysts, cosmetic materials, and luminescent materials.
In recent years, a method to form a thin metal film and a ceramic film using particles has attracted attentions.
The method allows to form a relatively high quality film by processes in room temperature with high-speed, thus, applications, such as for a piezoelectric element and a capacitor have been developing.
In particular, a method to form a ceramic film using particles is called an “Aerosol deposition method” and many applications have been developing.
There are various thin film deposition methods utilizing particles, and there are various names for the methods. Hereinafter, the Aerosol Deposition method (AD method) that has been recently used as a method to deposit a ceramic film will be uniformly used regardless of the materials.
In the AD method, powders (particles) are made into aerosol by carrier gas and the aerosol that includes particles and the carrier gas is injected from a nozzle to a substrate under low pressure (about several Torr) to form a film.
Pressure of a film formation chamber (deposition chamber) is one digit or more lower than that of a powder chamber. Thus, aerosol injected from the nozzle reaches to sonic speed. Accordingly, the particles collide with the substrate at substantially maximum sonic speed. As a result, a dense film is formed over the substrate.
The following publications may be referred for related techniques: Japanese Laid-open Patent Publication No. S59-80361, Japanese Patent No. 2963993, Japanese Laid-open Patent Publication No. 2001-79505, Japanese Laid-open Patent Publication No. 2002-214065, Japanese Laid-open Patent Publication No. H6-33241, and Stephen Wall et al., “Measurements of Kinetic Energy Loss for Particles Impacting Surfaces”, Aerosol Science and Technology, Vol. 12, pp. 926-946 (1990).
The AD method enables to form a dense film over a substrate by making particles collide with the substrate with high speed. However, particles reach to the substrate with high speed and thereby, many of the particles are rebounded from the substrate.
Accordingly, among the particles injected from the nozzle, those used for forming the film is very small and the use efficiency is typically 1% or less. Under the present circumstances, prepared powders are mostly wasted.
As illustrated in FIG. 16, the rebounded particles are gone off in the deposition chamber or over the substrate, thereby contaminate the chamber or the substrate. In other words, the rebounded particles may become a source of contamination. In particular, contamination of the substrate to be formed is not acceptable for electronic device applications.